Can you please check the below,
- Have you pre-staged the CNO object?
- Can you try creating IP-Less DAG and check if the issue still persists
- Make sure the firewall communication between the Exchange servers are allowed
- Try disabling windows firewall/AV on the exchange temporarily and check again
- If you have multiple NIC's, make sure it uses the primary NIC for the communication
- Uninstall the failover cluster manager, disable IPv6 using registry, reboot the server and then try adding it
Disabling IPv6 using registry, HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\TCPIP6\Parameters
Set DisabledComponents to ffffffff
Please Note: Take the backup of the registry before making changes and be careful in the changes as the improper configuration would lead to other issues.
Also, its not recommended to disable IPv6, this is only for addressing this issue and check if this resolves. I fixed the similar issue in an environment by disabling IPv6 and once the node is added successfully, I re-enabled it again.
- Check the GPO for any deny policy on the local logins because a local user account CLIUSR will be created
Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> User Rights Assignment -> Deny Log on Locally
"Now we also can't add any servers to the 2013 DAGs in the lab. We've been making some changes around AD, but we still haven't figured it out."
Could you please explain what changes are done in AD and are you trying to add both Exchange 2013 & 2019 in same DAG?
Cluster service will be installed while installing the Failover cluster manager and it will start once the node is added to the DAG. Cluster service wont start event is triggered because the node is trying to join DAG and it will attempt to start it. So, this can be ignored for now unless it is still populating even after the node is joined.